1. Field of the Invention
The present invention relates to an optical disc, and more particularly, to an optical disc having at least one recording layer, and apparatuses and methods for recording and reproducing data on the same.
2. Description of the Related Art
Compact discs (CDs) and digital versatile discs (DVDs) are the most popular types of data storage media. In general, user data is recorded on pits of a recording layer of a read-only optical disc and recorded by changing a phase of a phase change material (PCM) on the recording layer of a rewritable optical disc which is covered with the PCM.
A pickup, which is included in an, optical disc reproducing apparatus, detects a precise position of a track in which the user data is recorded, receives a laser beam reflected from the track, and reads the user data from the laser beam. A signal that the pickup uses to detect a position of a desired track is called a tracking signal. The tracking signal is obtained when a photo diode, which has a plurality of light receiving parts, receives the laser beam. Signals are generated from lights received by the respective light receiving parts, and then, the signals are added together or subtracted from each other. The tracking signal curves like an S-shape and right and left sides of the tracking signal, which are divided with respect to a central point of the tracking signal, have opposite polarities.
The polarities of the tracking signal change according to a type of the optical disc or physical characteristics of the recording layer on the optical disc, such as the physical characteristics of the pit or the track. In other words, the polarities of the tracking signal change from (−) to (+) and from (+) to (−) according to the type of optical disc or the physical characteristics of the recording layer. Therefore, when the optical disc is loaded into a conventional optical disc reproducing apparatus, the apparatus determines the polarity of a tracking signal by trial and error, detects the position of the track in which the user data is recorded based on the polarity, and reads the user data from the track. That is, the conventional optical disc reproducing apparatus spends considerable time in detecting the polarity of the tracking signal before reading the user data, thereby delaying a reproduction of the user data.
Meanwhile, a reflectivity of the optical disc is a ratio of a power of the laser beam reflected from the recording layer of the optical disc to the power of the laser beam incident on the recording layer. The reflectivity also depends on the type of optical disc or the physical characteristics of the recording layer, and therefore, the conventional optical disc reproducing apparatus detects the reflectivity by trial and error.